In Situ Construction of Functional Customized Elastic Li ⁺ Conducting Interlayer for High‐Performance Garnet‐Type Solid‐State Lithium Metal Batteries

Abstract Regulating the intrinsic volumetric fluctuations of lithium metal, ensuring efficient Li ⁺ transport, and suppressing detrimental dendrite growth remain critical challenges for the commercialization of solid‐state lithium metal batteries (SSLMBs). Therefore, the development of a multi‐dimensional interfacial engineering strategy is of paramount importance. Herein, a multifunctional elastic interlayer is designed to facilitate the diffusion of Li ⁺ by introducing phytic acid macromolecules (PA). The introduction of PA not only reinforces the mechanical robustness of the elastic skeleton, enabling it to effectively buffer the volume change during lithium deposition/stripping, but also modulates the solvation environment within the interlayer. This regulation promotes the formation of an anion‐rich solvation structure and constructs a stable SEI layer rich in LiF and Li _x PO ₄ on the surface of Li. Owing to the elastic interlayer and stable SEI, the assembled lithium symmetric cell achieves a high critical current density (CCD) of 4.6 mA cm ⁻² and maintains stable cycling for over 500 h at 1.0 mA cm ⁻² . Furthermore, the pouch cell incorporating with high‐loading NCM83 cathode retains a discharge capacity of 3.18 mAh cm ⁻² after 35 cycles, highlighting the practical potential of this interfacial design strategy.